Link circuit for interconnecting telegraph toll lines



July 4, 1933. G. s. VERNAM 1,916,239

LINK CIRCUIT FOR INTERCONNECTING TELEGRAPH TOLL LINES Filed May 21, 1951 1 FIG. 2

U I INVENTOR GILBERT S. V ERNAM ATTORN EY Patented July 4, 1933 I mm" stares Parr: T orricr.

GILBERT S. VERNAM, OF BLACTKENSACL, NEW JERSEY, ASSIG-NOR TO INTERNATIONAL.

OF NEW YORK, 1\T.. Y., A CORPORATION OF COMMUNICATIONS LABORATORIES, INC.,

, NEW YORK LINK CIRCUIT non rnrnnoonnnorme TELEGRAPH TOLL LINES Application. filed May 21,

This invention relates enerally to printing telegraph exchange systems, and more particularly to means in said systems for interconnecting telegraph toll lines, terminating in terminal telegraph repeaters, by means of link circuits in which the usual single line repeaters are omitted.

Heretofore, in connecting telegraph toll lines by means of link circuits, it has been necessary to. use a single line repeater in these circuits. Such use was necessitated by the fact that the loop circuits extending from the terminal telegraph repeaters to the toll board are normally arranged so that the current flows in a definite direction. l/Vhen current of the same polarity is connected in the same manner to all of the individual loop circuits, it is obvious thattwo loop circuits cannot be connected directly, since no current can then flow through the connected loop circuits.

One expedient to overcome this difficulty is to provide acsingle line repeater in the cord circuit so as to independently close each of the loop circuits through the operating relays of this repeater when the cord circuit is connected to the toll line loops. As each of the loop circuits is independently connected through one-half of the single line repeater in the cord circuit, the cord circuits can be used for interconnecting any two loop circuits, and to maintain the proper direction of current flowing through those circuits, even though the same polarity of battery is used in all loops. It is, therefore, ap-

parent that when a single line repeater is employed in the cord circuit, the maximum of flexibility is achieved in interconnecting the various loop circuits.

Another possible e-Xpedientis to connect one polarity of battery to partof theloop circuits and the opposite polarity'ot battery to the remainder of the loop circuits. This expedient is successful in eliminating the repeater .111 the cord circuit lnsofar as connections between loop circuits n winch the battery polarity is opposite are concerned. But

when connection is sought to be established between those loop circuits having the same polarity of battery, it is still necessary to 1931. Serial No. 538,982.

use a single line repeater in the cord circuit. Moreover, as some of the cord circuits in this system are provided with single line repeaters and others are not, this condition leads to the possibility of confusion on the part of the One of the principal objects of the present invention is to provide means for interconnectmg telegraph toll lines by means of link circuits in which the single line repeater is omitted, even though each toll line terminates in a telegraph repeater and each repeater is connected to a toll board by a closed local loop circuit in which the current flows in a single-direction.

Another object is to provide means for connecting two half-duplex loops in series without reversing the current through the windings of either of the polar sending relays contained in these loops.

A further objectis to provide means for connecting the loops extending from the terminal telegraph repeaters in such a way that monitor printers having polar printing magnets or polar relays can be used for monitormg purposes. I

Other objects will appear from the following detailed description and from the appended claims, as well as from the accompanying. drawing, in which:

Fig. 1 discloses schematically the general arrangement of a system in which this vinvention is embodied, and

Fig. 2 illustrates in detail the apparatus and circuits at an intermediate central oflice.

In general, the present invention may be employed in printing telegraph systems in which manual or semi-automatic means are employed for interconnecting subscribers -,stations.- For example, this invention might may be regarded as an improvement upon that system in that it provides for interconnecting two remote central oflices through an intermediate central office. In applying this invention to the system disclosed in the Connery application, some modification of the toll board circuit is required and also the addition 0 fa group of cord circuits, as will be described in more detail later.

Referring to Fig. 1, A and E designate subscribers stations; B designates a first central ofiice as disclosed in the Connery application; C designates an intermediate central oflice as disclosed in detail in Fig. 2 of the accompanying drawing and comprises a first toll line terminal 1 and a second toll line terminal 2 which are adapted to be interconnected by means of a link circuit; and D designates a central office as disclosedin the Connery application. The present invention would be employed when a communication circuit is extended fromA through B to C and then successively through C and D to E. The extension of this circuit is not in itself novel, but the novelty resides in the method of interconnecting the toll lines extending from B to C1 and from C2 to D without employing a single line repeater in the cord circuit connecting C1 and C2. i

'Referring to' Fig. 2, W designates a cord circuit, X a monitor printer unit, Y the toll board termination of a telegraph toll line, and Z a half-duplex set co-operatively associated with the toll line. Associated with Y and identical with it is another toll line terminal (not shown), and associated with this other toll line is a half-duplex set identical with Z. This other toll line and half-duplex set, as well as the numerous jackson the toll board, the cord circuits, and other half-duplex sets Z, etc., are omitted in order to simplify the description. It is to be noted, however, that all of the necessary elements of the system are disclosed in the drawing and it is to be understood that such elements can be readily multiplied to provide a switching system capable of handling any required number of toll calls.

The toll line terminal Y'includes the monitor jack 14 and the line jack 10, a marginal relay 11 for removing battery 12 from the loop circuit 33 and for grounding that circuit independently of the line ack 10, a relay 13 in the loop circuit 33 for operating a slowoperating relay 15 which relay in turn is adapted to light calling and supervisory lamp 16. The'loop circuit, it may be noted,

normallyextends from grounded battery 12,

contact A of marginal relay 11, winding of relay 13, contact B of monitor jack 14:, con-- tact A of relay 19, winding A of polar sending relay v18 of thehalf-duplex set Z, contact D of marginal relay 11 through contact Aof line jack 10 and a resistance to ground. This half-duplex set, which is of the usual type, includes a polar sending relay 18, transmitting relay 21 controlled by the sending relay, and polar line relay 22 which controls relays 19 and 20. Relay 20 controls a potentiometer circuit 24 and relay 19 controls the local loop circuit 33. Under the control of relay 20, potentiometer circuit 2 1 is adapted to reverse thedirection of the biasing current through winding B of sending relay 18 and thereby prevents its operation during the reception of signals. The armature of the transmitting relay or pole changer 21 is differentially connected to line relay 22, one of the windings extending through artificial line 27 to ground, and the other extending through the line wire 28 to a similar line relay at a distant central oflice. This differential connection prevents relay 22 from responding to outgoing signals from transmittingrelay 21. As the operation of the half-duplex set Z is well known in the art, it is unnecessary to describe it in more detail here. It is to be observed that for the halfduplex set Z, any type of telegraph repeater or carrier channel terminal set adapted for single or half-duplex operation might be substituted.

The cord circuit 1V includes an answering cord 1, a calling cord 9 and sleeve relays 2 and 8 which are associated respectively with the sleeves of the answering an d calling cords. One terminal of the winding of relay 2 is connected to an armature of relay 8 and the normally open contact A associated with this armature is connected to grounded battery 4 through high resistance 6. This same battery is connected to the sleeve of the calling cord through low resistance 7 and winding of relay8. The tip of the answering cord 1 is connected through contact A of relay 2 and resistance 3 to ground, and is also connected to normally open contact B of relay 2. The tip of the calling cord is connected through normally closed contact C of relay 2 through resistance 5 to grounded battery 4.

The monitor printer X, which is of usual type, includes a plug 29, relay or printer magnets 30, transmitter contacts 31 and a break key 32 in series with the tip and sleeve of the plug 29. p

The extension of a circuit such as the one shown schematically in Fig. 1 will now be described. For purposes of illustration B may represent a Boston central oflice, C a New York and D a Chicago central ofiice, while A and E may each designate a subscribers station associated respectively with B and D. The subscriber associated with the Boston central oflice calls the concentration board operator at that central ofiice in -a manner disclosed in the above-mentioned application. ,Then the concentration board operator and the toll board operator in the Boston oiiice co-operate to extend the subscribers line over line 28 of Fig. 2 to the toll the New York central ofiice.

line terminal jacks Y of the toll boardflat To accomplish this "the Boston toll board operator opens line 28 in a manner described in the abovementioned, application, which causes the line relay22 to release relays 19 and 20, thereby opening the loop 33v at the New York oiiice in a manner well known in the art. This opening of loop 33 releases relay 13 and after several seconds slow-operating relay 15 is operated and locked. The operating c11 cuit may be traced from battery 17 windlng of relay 15, contact A of relay 13, contact A of monitor'jack14 to ground, and the locking circuit may be traced from thesame battery through winding of relay 15, contact Bof that relay to contact A of monitor jack 14 independently of relay 13 and to ground. The operation of relay 15 lights lamp 16 over an obvious circuit.

Upon seeing the lamp lighted the New York toll board operator inserts plug 29 of the monitor printer unit X in the monitor jack 14, thus placing the printer in series with the loop 33, releasing relay 15 andopen ing the lamp circuit at contact A of the monitor jack, and extinguishing lamp 16. The New York toll'board operator then operates his printer to signal the Boston toll board operator over line 28. and the. latter requests a connection with a toll line extending to the Chicago central office. Upon the receipt of this information, the New York toll board operator inserts the answering cord 1 of the cord circuit VJ into the line jack 10 of the toll board connected to the half-duplex set Z in which the Boston line terminates. I

It may be noted here that it is immaterial whether the answering cord 1 or the calling cord 9 be inserted in the line'jack 10. In either case the final result, when both cords 1 and 9 are connected to jacks in the toll boards, is precisely the same;

To resume, when answering plug 1 is inserted in line jack 10, ground through contact A of the line jack is removed from the loop circuit 33 and this circuit is grounded instead through tip of answering plug 1.

The loop circuit 33 associated with the half duplex set Z in which the Boston line terminates is thus held closed over a circuit extending from grounded battery 12', contact A of marginal relay 11, relay 13, sleeve of moves the monitor printer unit X from the Boston circuit and plugs it intothe monitor jack 14 associated with the Chicago toll line.

This places the printer unit in series with York toll board.

' The. New York toll board operator then plugs the calling cord 9 of the cord circuit W into the line jack 10 associated with the Chicago line. The relay 8 and low resistance 7 are thus connected in series'with marginal relay 11 in the sleeve of the line ack 10 of the Chicago line and, as relay 11 is marginal and arranged to operate in series with the low resistance 7, these two relays operate over a circuit extending from grounded battery 4, low resistance 7, relay 8, sleeve of calling cord 9, sleeve of line jack 10, winding of relay '11 to ground. The operation of relay 11 by closing its B and C contacts removes battery 12 from the loop circuit extending to the half-duplex set in which the Chicago line terminates, connectsthis loop circuit to grounded battery4 in the cord circuit W and grounds this loop circuit independently of the tip of line jack 10. The complete cir-. cuit may be traced from grounded battery 4, contact C of relay 2, tip of calling plug 9, tip of'line jack 10,,conta-ct B of relay'11, relay 13, sleeve of monitor jack 14, printer set X, tip of monitorjack 14, contact A of relay 19, sending relay 18, contact C of relay 111, to ground. The operation of relay 8 completes an obvious circuit for relay'Q and marginal relay 11 in the loop associated with the Boston line and the former operates. though the latter does not because of the high resistance 6 in its circuit. The operation of-relay 2 extends the loop circuit 33 extending from the half-duplex set in which the Boston line terminates from tip of line jack 10, tip of answering cord 1, contact B of relay 2 to tip of calling plug 9, tip of line jack 1O associated with the Chicago line, contact B of operated marginal relay 11, winding of relay 13, sleeve of monitor jack 14, printer X, tip of monitor jack 14, contact A of relay 19',

winding of sending relay 18, contact C ofmarginal relay 11 to ground. The loops of the half-duplex sets in which the Boston and Chicago lines, respectively, terminate are thus connected in series and the two halfduplex sets thus combined form, in effect, a

station associated with the Chicago central ofiice in the manner described in the abovementioned application. As soon as it is evident that the Boston and Chicago operators are in satisfactory communication with each other, the New York operator may disconnect his monitor printer by withdrawing plug 29. The Chicago toll board operator then informs the Boston toll board operator that the circuit to the called subscribers station has been completed. After testing this circuit, the Boston toll board operator connects the calling subscriber to the New York line in a manner described in the above-mentioned application, and signals to the calling subscriber to go ahead. A communication circuit is thus established between the calling subscribers station in Boston and the called subscribers station in Chicago. '1

It is to be noted that the operation of the marginal relay 11in the toll board connected with the Chicago line alone permits the loops associated with both of the half-duplex sets to be connected in series without reversing the current through either of the polar sending relays 18 and also without reversing the current through the monitor jacks 1 1 on both of the toll boards. Both of these properties of the present invention are important for the reason that the half-duplex sets cannot be operated in series unless the current through the sending windings 18, when connected in series, is in the same direction as the current which flows through those relays when the loop circuits are not so connected, while the fact that the loop current invariably flows through the monitor-jacks M in the same direction permits the printer unit X to be readily used for monitoring purposes, even if it is equipped with a polar line relay or polar magnets 30.

If the calling cord 9 of the cord circuit X is used in answering the call from the Boston central office, the sleeve relay 8 and the marginal relay 11, associated with the loop 33 that extends to the halt-duplex set in which the Boston line 28 terminates, will be operated in series over a previously traced circuit. The said loop will then be extended to the cord circuit IV over a circuit previously traced. \Vhen the answering cord 1 is plugged into the line jack 10 associated with the Chicaco line, sleeve relay 2 will be operated immediately, since its circuit had previously been closed by the operation of relay 8. Thus, the two loop circuits, associated with the Boston and Chicago lines, are connected in a single series circuit as they werewhen the answering and not calling plug was inserted in the line jack asso ciated with the Boston line.

lVhen the communication between the calling and called-subscribers has ended, the

thereby lighting calling and supervisory lamp 16 at all of the central oflices. The toll board operators at these offices will then in sert their printer units X into the monitor jacks 14 at their respective stations. The insertion of the printer unit X extinguishes the lamp 16 and releases slow-operatin relay 15. The toll board operator at the oston oflice will then challenge to see if the call has terminated. Upon receiving an afiirmative answer, he will disconnect his circuit extending to the calling subscriber and ascertain that the toll board operators at New York and Chicago have received the information that the 'call has terminated, and upon receipt of this message these operators will pull down their cord circuits. \Vhen the toll board operator at the New York ofiice pulls down cord circuit WV, the removal of the calling cord 9 from the line jack 10 in the board associated with the Chicago line will release marginal relay 11 and close contact A of line jack 10, thus restoring the loop circuit 33 to normal, while the removal of answering cord 1 from the line jack 10 of the board associated with the Boston line will close contact A of the line jack and thus restore the loop circuit 33 of that board to normal. The toll boa-rd operators at Boston and Chicago restore in a manner described in the Connery application.

What is claimed is:

1. In a telegraph system, a pair of telegraph channels each having associated therewith a terminal telegraph repeater provided with a normally closed local loop circuit, a source of current of the same polarity for each of said loop circuits, a link circuit for interconnecting said loops, and means responsive to said interconnection for connecting said loop circuits in a single closed circuit.

2; In a printing telegraph exchange system, a pair of telegraph channels, each having associated therewith aterminal telegraph repeater provided with a normally closed loop circuit, a. polar sending relay in each loop circuit, a link circuit for interconnecting said loop circuits, and means responsive to said interconnection for connecting said loop circuits in series without reversing the current through either of said polar sending relays. v

3. In a printing telegraph exchange system, a plurality of telegraph channels, a switchboard having a plurality of monitor jacks, a terminal telegraph repeater associated with each channel, each repeater having a normally closed loop circuit extending through a monitor jack on said board, a link circuit for interconnecting said loop circuits, and means responsive to said interconnection for connecting said loop circuits in series without reversing the current through either of said monitor acks.

4. In a printing telegraph exchange system, a pair of telegraph channels, each having associated therewith, a terminal telegraph repeater provided with a normally closed loop circuit, a polar sending relay in and a switching relay associated with each of said loop circuits, a link circuit for interconnecting said loop circuits, means responsive to said interconnection for operating only one of said switching relays to connect saidloop circuits in a single closed circuit without reversing the current flow through said polar sending relays.

5. In a printing telegraph exchange system, a pair of telegraph channels, each having associated therewith a terminal telegraph repeater provided with a normally closed loop circuit, a marginal relay associated with each of said loop circuits, a linkcircuit for interconnecting said loop circuits, relay means in said link circuit operable with one only of said marginal relays in response to said interconnection for connecting said loop circuits in a single closed circuit.

6. In a printing telegraph exchange system a plurality of telegraph channels each having associated therewith a terminal repeater, said repeater being provided with a normally closed local loop circuit terminating in a switchboard, a source of current of the same polarity for each of said loop circuits, a plurality of link circuits associated with said switchboard, and means responsive to the interconnection of any two of said loop circuits through any one of said link circuits for directly connecting said loop circuits in series and for maintaining the flow of current in said series circuit.

7. In a printing telegraph exchange system, a plurality of telegraph channels each terminating in a half-duplex repeater, a switchboard provided with a plurality of line and monitor jacks, each half-duplex repeater having a normally closed local loop circuit extending through one of said line and one of said monitor jacks, a plurality of link circuits each capable of interconnecting any two loop circuits through the corresponding line jacks, and means responsive to said interconnection for connecting said loop cir cuits in series without reversing the direction of current through their corresponding monitor jacks, whereby a monitor printer having a polar printing magnet can be employed for supervision through either of the corresponding monitor jacks before and after the interconnection of said local loops.

8. In a printing telegraph exchange system, a plurality of telegraph channels each terminating in a half-duplex repeater, each repeater having a normally closed loop circuit terminating in a switchboard, the direction of current flow in each loop circuit being the same as in every other loop circuit, a plurality of link circuits each capable of interconnecting any two loop circuits, and means responsive to said interconnection for con necting said loop circujts in series without reversing the direction 0. current in any part of said series circuit, whereby the interconnected half-duplex repeaters act as a single half-duplex repeater.

9. In a telegraph system, a pair of telegraph channels each having associated therewith a terminal repeater provided with a normally closed loop terminating in a switchboard, a source of potential of the same polarity for each loop, a link circuit co-operating with said switchboard for connecting said loops in a single closed circuit including only one of said sources of potential whereby the two terminal repeaters form a single repeater for retransmitting into one channel signals received over the other channel.

10. In a printing telegraph exchange system, a pair of telegraph channels each having associated therewith a terminal telegraph repeater provided with a normally closed 10- cal loop extending through avline and a monitor jack on an associated switchboard, a link circuit co-operating with said line jacks for connecting said loops in a closed series circuit without reversing the direction of current through the monitor jacks whereby a monitor printer having a polar print ing magnet can be employed for supervision through either monitor jack both before and after the interconnection of said local loops.

11. In a printing telegraph exchange systern, a pair of telegraph channels each having associated therewith a terminal repeat-er provided with a closed local loop terminating in a line ack on an associated switchboard, a source of potential of the same polarity for each loop, a marginal relay in the sleeve circuit of each line ack, a link circuit, having a pair of sleeve relays, co-operating with said switchboard, means in said link circuit for efi-ecting the operation of only one of said marginal relays and both of said link circuit relays when the link circuit is inserted in said line acks, the operated marginal relay and the operated link circuit sleeve relays co-operating with said link circuit to connect said loops in a single closed circuit including only one of said sources of potential whereby the two terminal repeaters form a single repeater for retransmitting into one channel signals received over the other channel.

In witness whereof, I hereunto subscribe my name this 20th day of May, 1931.

GILBERT S. VERNAM. 

